Coating apparatus and liquid surface detecting method

Abstract

Disclosed is a coating apparatus configured to properly detect a liquid surface of a coating liquid stored within a slit nozzle. The disclosed coating apparatus includes a slit nozzle, a moving mechanism, a storage portion illumination unit, and an imaging unit. The slit nozzle includes an elongated main body, a storage portion configured to store a coating liquid within the main body, and a slit-shaped ejecting port configured to eject the coating liquid fed from the storage portion through a slit-shaped flow path, wherein at least a part of each of a first wall and a second wall which face each other in the main body is formed of a transparent member. The moving mechanism is configured to move the slit nozzle with respect to a substrate. The storage portion illumination unit is configured to illuminate an inside of the storage portion through the transparent member of the first wall. The imaging unit is configured to image the inside of the storage portion through the transparent member of the second wall.

What is claimed is: 
     
       1. A coating apparatus comprising:
 a slit nozzle including an elongated main body fixed to a fixing member, a storage tank having a first wall and a second wall facing with each other and configured to store a coating liquid within the main body, and a slit-shaped ejecting port configured to eject the coating liquid fed from the storage tank through a slit-shaped flow path to an upper surface of a substrate, at least a part of each of the first wall and the second wall being formed of a transparent member and at least two reference portions being formed on a surface of the second wall; 
 a moving mechanism including a substrate holding unit formed with a suction port configured to hold the substrate in a horizontal direction and a driving unit including a first motor configured to move the substrate holding unit in a horizontal direction with respect to the slit nozzle; 
 an elevating mechanism extending in a vertical direction and including a second motor configured to move the slit nozzle fixed to the fixing member in the vertical direction; 
 a first light source fixed to the fixing member to be positioned at a side of the first wall of the storage tank, and configured to irradiate light toward an inside of the storage tank through the transparent member of the first wall; 
 a second light source fixed to the fixing member to be positioned at a side of the second wall of the storage tank, and configured to irradiate light toward the surface of the second wall where the at least two reference portions are formed; 
 a camera fixed to the fixing member to be positioned at the side of the second wall of the storage tank and configured to capture either one of an image of the inside of the storage tank through the transparent member of the second wall or an image of the surface of the second wall where the reference portions are formed; and 
 a controller configured to control an overall operation of the coating apparatus including the slit nozzle, the moving mechanism, the elevating mechanism, the first light source, the second light source, and the camera, 
 wherein the controller is configured to:
 capture the image of the surface of the second wall where the reference portions are formed while the second light source irradiates the light toward the surface of the second wall where the reference portions are formed and the first light source is being turned OFF; 
 capture the image of the inside of the storage tank while the first light source irradiates the light toward the inside of the storage tank through the transparent member of the first wall and the second light source is being turned OFF; and 
 calculate a pixel size from the images captured by the camera thereby detecting a liquid surface of the coating liquid in the storage tank. 
 
 
     
     
       2. The coating apparatus of  claim 1 ,
 wherein the reference portions being used for calculating the pixel size of the images captured by the camera based on a number of pixels between the reference portions and an actual distance between the reference portions. 
 
     
     
       3. The coating apparatus of  claim 2 , wherein the second light source obliquely irradiates a light toward the surface of the second wall which faces the camera. 
     
     
       4. The coating apparatus of  claim 1 , wherein the camera captures the liquid surface of the coating liquid stored in the storage tank from an upper side or a lower side of the liquid surface, and
 when a plurality of liquid surface lines is included in the image captured by the camera, the controller is further configured to determine a liquid surface line located at an uppermost position among the plurality of liquid surface lines as the liquid surface. 
 
     
     
       5. The coating apparatus of  claim 4 , wherein the controller is further configured to determine whether the liquid surface is flattened based on the liquid surface line. 
     
     
       6. The coating apparatus of  claim 5 , wherein the controller is further configured to determine that the liquid surface is flattened when a difference in height of liquid surfaces at least at left and right end portions of the image is less than a threshold value. 
     
     
       7. The coating apparatus of  claim 6 , wherein the controller is further configured to divide each of the left and right end portions into a plurality of areas, and use an average value of liquid surface levels of the plurality of areas except for areas having highest and lowest liquid surface levels in each of the left and right end portions, as a liquid surface level of each of the left and right end portions. 
     
     
       8. The coating apparatus of  claim 1 , further comprising a brightness switch configured to switch a brightness of the first light source between a first brightness and a second brightness which is higher than the first brightness,
 wherein the first brightness is a brightness in a case where a transparent coating liquid is stored in the storage tank, and the second brightness is a brightness in a case where a coating liquid other than the transparent coating liquid is stored in the storage tank. 
 
     
     
       9. The coating apparatus of  claim 1 , wherein at least one of the first light source and the second light source is formed with a charge coupled device (CCD). 
     
     
       10. The coating apparatus of  claim 1 , wherein the transparent member is one of a glass or an acrylic resin. 
     
     
       11. A method of detecting a liquid surface in a slit nozzle including an elongated main body fixed to a fixing member, a storage tank having a first wall and a second wall facing with each other and configured to store a coating liquid within the main body, and a slit-shaped ejecting port configured to eject the coating liquid fed from the storage tank through a slit-shaped flow path to an upper surface of a substrate, at least a part of each of the first wall and the second wall being formed of a transparent member and at least two reference portions being formed on a surface of the second wall, the method comprising:
 providing a first light source and a second light source in each of a side of the first wall and a side of the second wall, and providing a camera in the side of the second wall; 
 capturing an image of a surface of the second wall where the at least two reference portions are formed using the camera while irradiating light toward the surface of the second wall by the second light source and the first light source is being turned OFF; 
 imaging capturing an image of the inside of the storage tank unit using the camera through the transparent member of the second wall of the storage tank while irradiating light toward the inside of the storage tank by the first light source through the transparent member of the first wall and the second light source is being turned OFF; 
 calculating a pixel size from the image captured at the capturing the surface of the second wall and the image captured at the capturing the inside of the storage tank; and 
 determining a liquid surface of the coating liquid stored within the storage tank based on the pixel size calculated at the calculating. 
 
     
     
       12. The method of  claim 11 , wherein, in the irradiating light toward the inside of the storage tank, the inside of the storage tank is irradiated with a first brightness when a transparent coating liquid is stored in the storage tank, and the inside of the storage tank is irradiated with a second brightness which is higher than the first brightness when a coating liquid other than the transparent coating liquid is stored in the storage tank. 
     
     
       13. The method of  claim 11 , wherein in the irradiating light toward the transparent surface of the second wall, the second light source obliquely irradiates the light toward the transparent surface of the second wall. 
     
     
       14. The method of  claim 11 , wherein the calculating further comprising dividing an actual distance between the reference portions by a number of pixels between the reference portions.